Shellfish on occasions become very poisonous by the consumption of poisonous marine dinoflagellates. Persons consuming the shellfish at this particular time become poisoned resulting in paralysis and if the dose is sufficient death may occur within 2 to 12 hours from severe paralysis and respiratory failure. These particular dinoflagellates, that sometimes grow out to red tide proportions, are mainly the species Gonyaulax catenella, G. tamarensis, and G. acatenella and in general are found along the northern coasts of North America, Europe, and Asia and along the southern coasts of South Africa and New Zealand. An outgrowth of these organisms may last 2 to 4 weeks during which time the shellfish will be poisonous. No antidote for the poison is known. The poison from one of these organisms, G. catenella, has been purified and found to be a substituted tetrahydropurine base. The objectives of the proposed work are mainly (a) to culture the organisms to obtain the poison, (b) to purify and determine the structure of the poison(s), (c) to study variations in the structure in relation to toxicity with the hope of finding an antidote for the poison, and (d) to study the mechanism of biosynthesis of the poison(s). Culturing of the organisms is carried out in artificial sea water. The organisms are filtered from the water and lysed with acid to release the poison. Purification of the poison will be accomplished with various chromatographic techniques. Studies on the chemical structure of the poisons will be carried out using the most modern instrumental techniques available at the University.